The invention relates to a transmission having a main shaft and a countershaft.
From the prior art, transmissions are already known having one input shaft, one main shaft, one countershaft and one output shaft in which in the input shaft, the main shaft and the output shaft are mounted on a common axis of rotation. Transmissions of this kind can have a one piece input and output shaft or a one piece main and output shaft. A transmission of this kind is shown, e.g. in DE 195 38 192.
The numbers of teeth on the gear wheels of the shafts are determined on the basis of the desired reduction ratios. This implies specific diameter ratios of the gear wheels of the parallel shafts relative to each other and thus also the spatial distance between the shafts. Thus the gear wheel pair consisting of the first gear wheel upon the input shaft and the first gear wheel upon the countershaft, seen from the input side, are configured so that a gear wheel of very small diameter upon the input shaft is associated with a gear wheel of very large diameter upon the countershaft. This pair of gear wheels makes a transmission of a great torque at a lower speed level possible, but a great spatial distance results in a large size of the transmission housing which can lead to difficulties in the installation space for the vehicle manufacturer.
The problem on which the invention is based is to reduce the installation space needed for a transmission and lead to a smaller size of the transmission.
It is proposed, according to the invention, to non-rotationally mount a gear wheel, upon the output shaft of the transmission, which is driven by a gear wheel non-rotationally connected with the countershaft, the gear wheel pair forming one constant. The input shaft of the transmission is non-rotationally connected with the main shaft. The axis of rotation of the input shaft and the axis of rotation of the main shaft are equal and the axis of rotation of the main shaft and the axis of rotation of the output shaft do not form the same axis. The distance between the axes of rotation of main shaft and output shaft is determined by the reduction ratio of the gear wheel pair of the constant.
In an advantageous development, the gear wheel pair of the constant is lodged in a separate transmission housing in order to make replacement of the gear wheel pair possible.
In another advantageous development for driving a hydrodynamic retarder, an auxiliary output shaft is provided which can be driven directly by the main shaft or the countershaft and serves to achieve a high rotational speed of the retarder without intercalation of a high driving step.
For a splitter transmission, an advantageous development shows upon the output shaft when a gear shift device subdivides the gear steps in half speed steps.
In an advantageous development, a range-change group transmission, in the form of a planetary transmission, is provided next to the gear wheel pair of the constant for enlarging the total spreading of the transmission.
By shifting the arrangement of a constant of the transmission to the output side end of the transmission and the non-coaxiality of the axes of rotation of main shaft and output shaft, the diameters of the large wheel of the transmission are reduced. With reduced diameters, the weight of the gear wheels thereby can be reduced and the axial distances of the parallel shafts shortened, which results in a smaller size for the transmission. A reduced size of the transmission means in this instance advantageously less weight and more installation space in the vehicle. At the same time, less expenditure in material and processing for smaller gear wheels and a housing results in lower cost. The smaller masses of the gear wheels to move and synchronize, when shifting, result in a level of shifting effort clearly. The synchronizing devices also are less apt to fail, since the masses to be synchronized are smaller. By virtue of the smaller gear wheels on the input-side end of the countershaft with a small axial distance between input shaft and main shaft and the countershaft, the rotational speeds of the countershaft are at a higher level. A reduced torque level, on which the structural parts of the transmission must be designed, is obtained thereby in the largest part of the transmission. A high torque only generates in the output constant when an enlarged axial distance exists between the output shaft and the countershaft. With the inventive arrangement, the transmission input torque can be designed the same size for transmission constructions having direct drive and overdrive versions.
As a result of a one piece design for the input shaft and the main shaft, the pivot bearing of the main shaft and the input shaft of the prior art can be eliminated. The gear wheel pair mounted on the transmission end can be configured so as to be inserted as a separate unit, after the other transmission housing, making a modular design of transmissions having different wheel pairs on the output constant possible.